Add PC 26.2 chunk implementation mapping

[DallasCarraher]

Summary

Minecraft 26.2 (protocol 776) uses the same chunk section format as 26.1, so it maps to the existing 1.18-family implementation here rather than needing a new one. Without this, prismarine-chunk throws No chunk implementation for pc 26.2 found for any consumer (mineflayer, etc.) as soon as minecraft-data has data for 26.2 — which it doesn't yet upstream, but does on the branch backing PrismarineJS/minecraft-data#1298.

Related work getting 26.2 fully usable end-to-end:

• PrismarineJS/minecraft-data#1298 — adds the 26.2 data itself
• This PR
• PrismarineJS/prismarine-physics#143 — 26.2 liquid gravity feature
• PrismarineJS/node-minecraft-protocol#1529 — login success packet sessionId
• PrismarineJS/mineflayer#4121 — 26.2 added to testedVersions

Test plan

• Full test suite against minecraft-data#1298's branch: 328/328 passing
• standard lint clean

[rom1504]

Astra agent review — AI-generated, not manually written by the maintainer.

Rechecked e3424f6 and the existing discussion.

This one-line factory dispatch addition looks ready for maintainer merge review. It routes 26.2 through the existing modern column implementation and leaves every older route unchanged; current CI passes.

It is independently reviewable, but #331/#334 contain overlapping dispatch entries. Choose one surviving hunk when landing them. Routing a version here does not by itself certify all companion 26.2 data or wire changes.

Skills used: prismarine-protocol-data-review checked the actual selected data and codec/version contract;prismarine-architecture-review checked shared ownership and compatibility; prismarine-review checked current scope and existing feedback to avoid duplicate threads.

[DallasCarraher]

Thanks for the review. Noted that #331/#334 carry an overlapping dispatch entry. This PR is the standalone one-line dispatch addition, so I'll drop the duplicate hunk from #334 so only one surviving entry remains when these land.